Movement of calcium ions across cell membranes is a critically important event in the normal functioning of excitable tissues such as vascular smooth muscle, cardiac muscle, and the central nervous system. Influx of calcium ions through specialized channels in the cell membrane regulates the release of substances such as hormones and neurotransmitters.
Drugs that interfere with calcium influx in neurons are used in the treatment of the pain. In the treatment of hyperalgesia and alodinia it has been suggested that drugs that block calcium channels are more effective in the treatment of the pain than antagonists for individual receptors as NMDA, BK1, NK2 and CGRP. This advantage is due to the fact that calcium channel blockers do not develop tolerance as morphine does and they interfere with the release of neurotransmitters involved in nociception. With the exception of an omega-conotoxin ziconotide, disclosed in WO 9954350, and isolated from the snail Conus magnus no other drug with sufficient specificity or potent effect on the diverse forms of pain is known.
Patent document U.S. Pat. No. 6,489,298 relates to contulakin-G, analogs thereof and uses thereof in the native form or cDNA in formulations with application in pain processes associated with thrombosis, gastrointestinal disorders, analgesia, ulcers, tumors.
In WO02079236, an alpha-conotoxin peptide is used in the treatment or prevention of pain, in recovery from nerve injury, and in the treatment of painful neurological conditions. Alpha-conotoxin peptides are also described as being useful for muscle relaxation and neuromuscular blocking agents, in U.S. Pat. No. 6,268,473.
Technologies related to spider toxins are also found in the prior art. Document EP1161951 describes the toxin of spider Selenoscomia huwena, the peptide of which can be applied parenterally or topically in the treatment of pain and inhibition of calcium channel activity.
Patent document U.S. Pat. No. 5,281,693 discloses methods and compositions with the use of oligonucleotides obtained from the toxin of spider Agelenopsis aperta, for blocking Ca2+ channels, and their use in the treatment of neurological disorders.
More common is the use of morphine and derivatives thereof with wide application in the treatment of nociceptive processes and analgesia procedures. However, its efficacy is for a short period of time, requiring new doses. In view of new technologies with a large spectrum of action and duration, the possibility of developing tolerance to the medication reduces its application.
As already mentioned above, the movement of calcium ions regulates contraction of heart muscle and vascular smooth muscle in the wall of the blood vessels. Abnormal influx of calcium ions has been reported to play a role in the pathogenesis of various cardiovascular disorders (e.g. anoxic/ischemic heart disease, cardiac arrhythmias) and drugs capable of blocking the movement of calcium through calcium channels have been used for treatment of pain, cardiac arrhythmias, coronary artery diseases, cardiopathy and stroke.
The current used drugs, however, have non-specific physiological effects and varying tissues specificities that can lead to undesirable side-effects in patients. Moreover there are several known subtypes of calcium channels with varying physiological actions and no drug that specifically bocks certain of these subtypes is known.
Phα1β was more effective to inhibit pain without causing severe side effects as those observed with ω-conotoxin zicononotide. This toxin-induced antinociception caused on the animals side effects such as serpentine tail movements, body shaking and allodynia that were not observed with analgesic doses of Phα1β.
Phα1β injected intrathecally has a potent and longer antinociceptive effect on the inflammatory phase of formalin test than ω-conotoxin ziconotide. Thus the analgesic effect of Phα1β lasted for a longer period of time than that observed for ω-conotoxin ziconotide.
The spinal dose-response curves showed that Phα1β displayed lower ED50 values for inhibiting the inflammatory phase of formalin test, than that observed with ω-conotoxin ziconotide.
In the nervous system, calcium influx into the presynaptic nerve terminal via calcium channel is a necessary prerequisite for the release of chemical neurotransmitter at synapses and thus for the proper functioning of these synapses. Lowering the extracellular calcium is routinely used by neurophysiologist to reduce or abolish synaptic transmission in isolated pieces of nervous tissue.
ω-conotoxin ziconotide and Phα1β caused inhibition of the capsaicin-induced increase of [Ca2+]i, which plays an important role in neurotransmitter release, by blocking N-type calcium channels on neuronal pre-synaptic membrane.
Phα1β presented higher efficacy than ω-conotoxin ziconotide to inhibit capsaicin-induced release of glutamate from nerve ending spinal cord of rats.
Most important, the antinociceptive effects of Phα1β were observed using doses that were around 15 times lower than those associated with side-effects (DT50).
The recombinant form of Phα1β expressed in E. coli was capable to repeats the antinociceptive effects of the native toxin.
Phα1β may have a superior efficacy profile for relief of persistent pathological pain states than ω-conotoxin MVIIA.
Phα1β also showed higher efficacy than conotoxins against pain induced on the hot plate test. On this model of pain, Phα1β elevates thresholds, increasing significantly the latency period to 3, 4, 5, 6 and 24 hours after its administration In contrast, morphine only produced a significant effect that was initiated faster, but only lasted for up to 5 hours, a shorter time.
It has not been possible, however, specifically to affect synaptic transmission in vivo in the central nervous system (CNS) by manipulating the function of neuronal calcium channels. With the exception of the omega-conotoxin ziconotide isolated from the venom of the marine snail no drug with sufficient specificity or potent effects on CNS calcium channels is known. Phα1B may have the same properties of omega-conotoxin ziconotide without having the side effects observed for omega-conotoxin ziconotide.
Abnormal influx of calcium is thought to be very important in the pathogenesis of several CNS disorders, including anoxic/ischemic (stroke) damage, epilepsy, and the neuronal death associated with chronic epilepsy. Again, the paucity of chemical agents that potently and specifically block CNS calcium channels has impeded the development of an effective drug therapy for these prevalent neurological problems.
Thus, it would be a very considerable improvement in the art if it were possible to develop chemical agents that specifically and potently block calcium channel function in the CNS. In particular it would be advancement in the art to provide a specific blocker of particular subtypes of calcium channel. Similarly it would be advancement in the art to provide a specific blocker of calcium channels in the CNS.
Such chemical composition and methods for their use are disclosed and claimed below.